In a large saucepan or microwave-safe bowl, melt butter and marshmallows.
Remove from the heat; stir in peanut butter.
Gradually add cereal; mix until well coated.
Spread and press into a greased 13-in.x 9-in.x 2-in.pan; set aside.
In a microwave-safe bowl or the top of a double boiler over simmering water, melt the chips.
Spread over cereal mixture.
Cover and freeze for 15-20 minutes or until chocolate is set.